Hafenhalle at the waterfront is always a guaranteed first class meal -At the higher end of the price range, but still much better value than anything this side of the border!
My 2 favourites are:
HEUBODEN
http://www.heuboden-kn.de/
Excellent meat up to XXL, great prices, laid back service - Family run, one chef and so the food can take a while, but it's always worth the wait. It's a ten minute drive away from the centre of Konstanz, so you'd need a map or public transport, not walking distance.
Filetsteak.........19,50€
Aus dem zartesten Teilstück vom jungen Rind 250g mit Kräuterbutter
T- Bone............26,00€
Zartes Filet und saftiges Roastbeef am T-Knochen, mit knusprigem Fettrand, 500g
mit Kräuterbutter
Add your veg or potatoes at around 3.50Euro and sauce for 3.00 and you've got a great 250g FILLET steak dinner for 30 francs!!

ZUR SCHWEIZER GRENZE (No website)
http://www.tripadvisor.de/Restaurant...rttemberg.html
Again, you'd need to drive here as it's just outside the centre, 5 mins drive direction Tägerwilen/Gottlieben (CH), right at the mainly unattended little border control.
Great family run restaurant with local produce, constantly changing seasonal specials and simply perfect food, every time i've been. Fantastic value and a good selection of local weins and beers too.
The game season right now I would especially recommend, it's brilliant and great value for money. Been a year since I was last there, but have eaten there at least ten times and from memory a large mixed game plate plus salad starter would be bewteen 20-25 Euro, again nothing compared to what we pay in CH.
The Indian restaurant that sits under the shadow of the catherdral is also very good.
Hope that helps!